Amplifier with configurable final output stage

Patent metadata

Field	Value
Publication number	US-9929703-B1
Application number	US-201615277465-A
Country	US
Kind code	B1
Filing date	Sep 27, 2016
Priority date	Sep 27, 2016
Publication date	Mar 27, 2018
Grant date	Mar 27, 2018

Abstract

An amplifier may include a first stage configured to receive an input signal at an amplifier input and generate an intermediate signal which is a function of the input signal, and a final output stage configured to generate an output signal which is a function of the intermediate signal at an amplifier output, and a signal feedback network coupled between the amplifier output and input. The final output stage may be switchable among a plurality of modes including at least a first mode in which the final output stage generates the output signal as a modulated output signal which is a function of the intermediate signal, and a second mode in which the final output stage generates the output signal as an unmodulated output signal which is a function of the intermediate signal. Structure of the feedback network and the first stage may remain static when switching between modes.

First claim

What is claimed is:

1. An amplifier comprising:
a plurality of stages comprising at least:
a first stage configured to receive an input signal at an amplifier input and generate an intermediate signal at an intermediate output which is a function of the input signal; and
a final output stage configured to generate an output signal at an amplifier output, wherein the output signal is a function of the intermediate signal; and

a signal feedback network coupled between the amplifier output and the amplifier input;
wherein the final output stage is switchable among a plurality of modes including at least:
a first mode in which the final output stage generates the output signal as a modulated output signal which is a function of the intermediate signal; and
a second mode in which the final output stage generates the output signal as an unmodulated output signal which is a function of the intermediate signal; and

wherein structure of the signal feedback network and the first stage remain static when switching between the first mode and the second mode and when switching between the second mode and the first mode.

2. The amplifier of claim 1 , wherein the final output stage is configured to switch between the plurality of modes based on a characteristic of at least one of the input signal and the output signal.

3. The amplifier of claim 2 , wherein the characteristic comprises at least one of a frequency of the input signal, an amplitude of the input signal, and a noise characteristic of the input signal.

4. The amplifier of claim 2 , wherein the characteristic comprises an amplitude of the output signal, and the final output stage is configured to switch between the first mode and the second mode when an amplitude of the output signal is approximately zero.

5. The amplifier of claim 2 , wherein the final output stage is configured to:
switch between the first mode and the second mode at an approximate completion of a modulation period of the modulated output signal; and
switch between the second mode and the first mode at an approximate beginning of another modulation period of the modulated output signal.

6. The amplifier of claim 1 , wherein a signal gain of the final output stage in the first mode is approximately equal to a signal gain of the final output stage in the second mode.

7. The amplifier of claim 1 , wherein an offset of the final output stage in the first mode is approximately equal to an offset of the final output stage in the second mode.

8. The amplifier of claim 1 , wherein a signal gain of the final output stage in the second mode is calibrated to match a signal gain of the final output stage in the first mode.

9. The amplifier of claim 1 , wherein an offset of the final output stage in the second mode is calibrated to match an offset of the final output stage in the first mode.

10. The amplifier of claim 1 , wherein the modulated output signal comprises a pulse-modulated signal.

11. The amplifier of claim 10 , wherein the pulse-modulated signal comprises one of a pulse-width modulated signal and a pulse-density modulated signal.

12. The amplifier of claim 1 , wherein the unmodulated output signal comprises a continuous-time baseband signal.

13. The amplifier of claim 1 , wherein when the final output stage is operating in the second mode, at least one of the signal feedback network and the first stage is modified to decrease a noise floor of the amplifier.

14. The amplifier of claim 1 , wherein:
the amplifier comprises a Class-D modulator; and
the final output stage operates as an open-loop switched-mode driver in the first mode and operates as a continuous-time closed-loop amplifier in the second mode.

15. The amplifier of claim 1 , wherein when the final output stage is operating in the second mode, the amplifier comprises a first feedback loop including the signal feedback network and a second feedback loop coupled between the amplifier output and the intermediate output.

16. A method for operating an amplifier having a plurality of stages comprising at least a first stage configured to receive an input signal at an amplifier input and generate an intermediate signal which is a function of the input signal, and a final output stage configured to generate an output signal at an amplifier output, wherein the output signal is a function of the intermediate signal, and a signal feedback network coupled between the amplifier output and the amplifier input, the method comprising, switching the final output stage among a plurality of modes including at least a first mode in which the final output stage generates the output signal as a modulated output signal which is a function of the intermediate signal, and a second mode in which the final output stage generates the output signal as an unmodulated output signal which is a function of the intermediate signal, wherein structure of the signal feedback network and the first stage remain static when switching between the first mode and the second mode and when switching between the second mode and the first mode.

17. The method of claim 16 , further comprising switching between the plurality of modes based on a characteristic of at least one of the input signal and the output signal.

18. The method of claim 17 , wherein the characteristic comprises at least one of a frequency of the input signal, an amplitude of the input signal, and a noise characteristic of the input signal.

19. The method of claim 17 , wherein the characteristic comprises an amplitude of the output signal, and the method comprises switching between the first mode and the second mode when an amplitude of the output signal is approximately zero.

20. The method of claim 17 , further comprising:
switching the final output stage between the first mode and the second mode at an approximate completion of a modulation period of the modulated output signal; and
switching the final output stage between the second mode and the first mode at an approximate beginning of another modulation period of the modulated output signal.

21. The method of claim 16 , wherein a signal gain of the final output stage in the first mode is approximately equal to a signal gain of the final output stage in the second mode.

22. The method of claim 16 , wherein an offset of the final output stage in the first mode is approximately equal to an offset of the final output stage in the second mode.

23. The method of claim 16 , further comprising calibrating a signal gain of the final output stage in the second mode to match a signal gain of the final output stage in the first mode.

24. The method of claim 16 , further comprising calibrating an offset of the final output stage in the second mode to match an offset of the final output stage in the first mode.

25. The method of claim 16 , wherein the modulated output signal comprises a pulse-modulated signal.

26. The method of claim 25 , wherein the pulse-modulated signal comprises one of a pulse-width modulated signal and a pulse-density modulated signal.

27. The method of claim 16 , wherein the unmodulated output signal comprises a continuous-time baseband signal.

28. The method of claim 16 , further comprising, when the final output stage is operating in the second mode, modifying at least one of the signal feedback network and the first stage to decrease a noise floor of the amplifier.

Assignees

• Cirrus Logic Int Semiconductor Ltd
• Cirrus Logic Inc

Inventors

• Zhao Xin
• Das Tejasvi
• Fei Xiaofan
• Morton Alan Mark

Classifications

• H03F2200/345

  Pulse density modulation being used in an amplifying circuit · CPC title

• H03F1/32 Primary

  Modifications of amplifiers to reduce non-linear distortion (by negative feedback H03F1/34) · CPC title

• H03F3/2173

  of the bridge type · CPC title

• H03F1/0277

  Selecting one or more amplifiers from a plurality of amplifiers · CPC title

• H03F2200/351

  Pulse width modulation being used in an amplifying circuit · CPC title